Printed Circuit Heat Exchanger Research Articles

Geometric and operational analysis of a heat recuperator operating with s-CO2 near the pseudocritical region

Heat recuperators are commonly used in numerous industrial processes, including power generation plants. Additionally, with interest in power cycles operating with supercritical fluids, such as carbon dioxide (s-CO2), a better understanding of heat exchangers operating with the hot and cold fluids near the pseudo critical points is needed. Therefore, this study models a printed circuit heat exchanger operating with s-CO2 on the hot and cold sides using a finite volume formulation. The model considers the convective resistances associated with the s-CO2 on both sides of the heat exchanger, as well as the conductive resistance due to the solid wall separating them. The recuperator’s behavior was analyzed while varying its geometrical (diameter, length and number of channels) and operational (inlet pressure and temperature on both sides) parameters. Thermal and hydraulic figures of merit were considered, such as the heat exchanger effectiveness, thermal conductance and pressure drop. The results showed that similarly to geometrical parameters, the operational conditions also had a significant effect on the figure of merits considered, especially near the pseudo critical line, a region characterized by major property changes. In addition, a multi-objective optimization process was implemented returning a series of optimal solutions, which were presented as a Pareto curve. Among the results obtained, it is worth mentioning that an optimum hot s-CO2 inlet temperature was obtained for the entire front at roughly 650 K, while there were a minimum number of channels and a cold s-CO2 inlet pressure, close to 155,000 and 15 MPa, respectively, limiting the Pareto front, which were related to the maximum effectiveness.

Optimization of zigzag parameters in printed circuit heat exchanger for supercritical CO2 Brayton cycle based on multi-objective genetic algorithm

The printed circuit heat exchanger (PCHE) shows promise for applications in the supercritical carbon dioxide (S-CO2) Brayton cycle due to its great resistance to high temperature and pressure. The zigzag channel is the typical channel configuration of PCHEs containing structural parameters such as pitch, bend angle, and bend radius that can significantly influence flow and heat transfer performance. In this study, the pitch, bend angle, and bend radius are selected as the design variables, while the pressure and heat exchange capacity are considered as the optimization objectives. Based on the non-dominated sorting genetic algorithm-II (NSGA-II), optimization work is conducted to improve the performance and size of the zigzag channel over a wide range of structural parameters. To predict local flow and heat transfer performance, the surrogate model embedded in the one-dimensional analysis code is proposed using the artificial neural network (ANN) method and trained by 144 groups of three-dimensional simulation results. The results calculated by the one-dimensional analysis code show that both the bend angle and bend radius can significantly affect the performance of the printed circuit heat exchanger, while the bend radius plays a more important role on the pressure drop. However, the effect of the pitch on the zigzag channel is relatively small. The optimization results indicate that the appropriate core length of the zigzag channel varies with the design of the outlet temperature. For the 0.4 m core length suitable for the 306 K outlet temperature, the size is 20% less than for a 0.5 m core length with similar flow resistance, and the pressure drop is 66.3% less compared to that of the 0.3 m core length. In addition, the zigzag channel with hybrid structural parameters is proposed and compared to the conventional zigzag printed circuit heat exchanger. The optimization results indicate that the maximum difference between the two objectives is only 4%. Thus, the zigzag channel with constant structural parameters can satisfy the demand for optimization with a simpler design.

Study on thermal deformation of hybrid printed circuit heat exchanger for advanced nuclear reactor

The intermediate heat exchanger (IHX) is one of the key components in advanced nuclear reactor power generation system. Printed circuit heat exchanger (PCHE) with mini-channels is a good candidate for the IHX. But the whole PCHE with tens of thousands of mini-channels is hard to be modeled and calculated at high temperature. Thus, the homogenization method, which can calculate the thermal deformation of the whole hybrid mini-channel PCHE, is conducted in this study and both the elastic and elastic-plastic finite element analysis methods are used. Here, the performance of the PCHE is assumed to be isotropic in the simulation. The results show that the macroscopic thermal deformation of the whole PCHE follows a gradually downward trend from hot side to cold side, while obvious thermal stress concentration is observed around the junctions between the PCHE core and cover plate. The stress and strain calculated by elastic and elastic-plastic methods under different constraints show quite different patterns. For the thermal deformation analysis of PCHE under weak constraint or small temperature difference conditions, the stress and strain results by elastic analysis and elastic-plastic analysis are similar so that the elastic analysis can be used. Under the strong condition, the stress of PCHE calculated by elastic analysis is much higher than that of elastic-plastic analysis, while the strain is lower than that of elastic-plastic analysis. The relative deviations of stress are 100.883% and 120.786% along path 1 and path 2 respectively. And the relative deviations of strain are 6.987% and 10.139% along path 1 and path 2 respectively. The elastic-plastic analysis should be used instead of the elastic analysis.

Fluid-Thermal-Mechanical Coupled Analysis and Optimized Design of Printed Circuit Heat Exchanger with Airfoil Fins of S-CO2 Brayton Cycle

Fluid-Thermal-Mechanical Coupled Analysis and Optimized Design of Printed Circuit Heat Exchanger with Airfoil Fins of S-CO2 Brayton Cycle

Numerical Investigation of Thermal-Hydraulic Performance of Printed Circuit Heat Exchanger with Different Fin Shape Inserts

The printed circuit heat exchanger is one of the most recent important heat exchangers, especially in the nuclear power plant and aerospace applications, due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation of the thermo-hydraulic performance of PCHE with a new non-uniform channel design configuration. The new channel design consists of two different fins and shape inserts: the diamond and biconvex shapes. The influence of two design parameters on the heat exchanger performance was studied and optimized, the longitudinal and transverse pitch length (Pl) and (Pt). Air with constant properties as the working fluid with constant heat flux at the walls envelope. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (Pl=20, 30, 40, and 50) mm and (Pt=3, 4, and 5) mm. Three performance parameters were studied the Nusselt number, friction factor, and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch lengths, and it was shown that this enhancement was found only at high Reynolds numbers above 1400. The higher enhancement factor was with NACA 0020 airfoil fins at pt=3 mm and pl=20mm of η=2.75 at Re=2000, while the worst performance was obtained with biconvex fins. The main reason behind the enhancement is the disruption of the boundary layer and the good mixing induced in the fluid flow.

Multi-objective optimization of printed circuit heat exchanger used for hydrogen cooler by exergoeconomic method

Hydrogen cooler is a key equipment of the precooling unit in hydrogen refueling stations with the requirement of high heat transfer efficiency, high compactness and high pressure resistance. Printed circuit heat exchanger is a promising candidate for the hydrogen cooler due to its great performance on extremely high pressure and high temperature working environment. In this paper, a hydrogen cooler with a thermal load of 72 kW is firstly designed by using the segmented thermal design method and logarithmic mean temperature difference method. Then, the capital model of the hydrogen cooler is established to evaluate the performance using the exergoeconomic method. The results show that the operating cost, which is related to exergy destruction, accounts for 94.5% of the total cost of the hydrogen cooler. The thermal exergy destruction accounts for 92.4% of the total exergy destruction. Finally, the geometrical parameters of the channel are optimized by using the multi-objective optimization. The channel radius shows the most significant impact on the construction cost and operating cost among the three geometrical parameters. Compared with the coaxial tube evaporators, the printed circuit heat exchanger has better performance on the volume and total cost, which are reduced by 88.0% and 4.0% respectively.

Investigation on Flow Maldistribution and Thermo-Hydraulic Performance of PCHEs with Spoiler Perforated Boards

In this study, the effects of the maldistribution coefficient on the thermo-hydraulic performance of discontinuous fin printed circuit heat exchanger (DF-PCHE) entrance head and channels are numerically investigated. To improve the flow uniformity at the entrance head, the flow in the exchanger with three types of spoiler perforated boards (SPBs) having 3 × 3, 4 × 4, and 5 × 5 holes and three kinds of hole diameters (Φd = 30, 25, and 20 mm), respectively, are compared to the flow in an exchanger with no SPB. The results show that a small maldistribution coefficient for the inlet velocity field is beneficial for the thermo-hydraulic performance of the DF-PCHE channels, and a maldistribution coefficient of 0.7 is an acceptable velocity distribution for the PCHE channel inlet. Using the 3 × 3 SPB with Φd = 30 mm, the maldistribution coefficient becomes 0.7, the fastest among all the SPB application cases at ΔL = 150 mm. Moreover, its heat transfer coefficient and pressure drop increase by 22.46% and decreases by 47.2% compared to those of the exchanger without SPB, respectively.

Study on thermal-hydraulic characteristics of CO2-water printed circuit heat exchanger with different structural parameters

• Simulation work is carried out to investigate the effect of structural parameter. • Separated flow shows high correlation with flow and heat transfer performance. • Comprehensive performance is compared among pitch, zigzag angle and bend radius. The printed circuit heat exchanger is a promising candidate in supercritical CO 2 Brayton cycle due to its advantages with high compactness and high resistance to pressure and temperature. In this paper, the simulation work of zigzag channel PCHE validated by experiment are conducted with different pitches (10 mm − 25 mm), zigzag angles (90° − 165°) and bend radius (0.2 mm − 7.0 mm) to investigate the thermal-hydraulic characteristics of zigzag channel PCHE using for precooler. Based on the 1/2 pitch-averaged results, it is found that the heat transfer performance and flow resistance change considerably with the variation of zigzag angle and bend radius. Meanwhile, the heat transfer coefficient and friction factor present a fluctuation change in local position. The high correlation is found between separated flow and friction factor based on the analysis of separated flow ratio. Besides, with the comparison of comprehensive factor PEC, the optimal structure of PCHE is inconsistent between the regions near and away from the pseudo-critical. Furthermore, the zigzag angle and bend radius appear to have greater influence than pitch on PCHE performance according to the analysis by noise performance statistics (NPS).

Numerical investigation on thermal–hydraulic performance of supercritical LNG in a Zigzag mini-channel of printed circuit heat exchanger

• Flow mechanism of supercritical hydrocarbon fluids was investigated. • Comparison on thermal performances for two hydrocarbon fluids was compared. • Correlations for supercritical hydrocarbon fluids in a mini-channel were proposed. Printed circuit heat exchanger (PCHE) is receiving wide attention as a new kind of compact heat exchanger. It is considered as a promising vaporizer in floating liquefied natural gas (FLNG) vessels due to its compactness and high efficiency. In this paper, the numerical model with two Zigzag mini-channels was built. The cross section was a semicircle with the diameter of 1.5 mm and the overall length was 200 mm. In the simulation, SST k - ω turbulent model was employed and validated against experimental data of supercritical CO 2 flow. The mechanism of flow and heat transfer was investigated, and the influence of operating parameters including mass flux, outlet pressure and inlet temperature was analyzed from the perspective of high-speed components of turbulent core area, degree of flow separation, energy transport and dissipation rate. The results indicated that the worse flow performance and better heat transfer performance exhibited at higher mass flux and inlet temperature conditions, whereas the higher outlet pressure conditions exhibited the better flow and heat transfer performances. Correlations for the Fanning friction factor and Nusselt number were developed within a deviation of ±5%, aiming to apply to the prediction of thermal–hydraulic performance of supercritical LNG.

Numerical Investigation on Thermal–Hydraulic Performance of a Printed Circuit Heat Exchanger for Liquid Air Energy Storage System

A printed circuit heat exchanger (PCHE) is utilized to cool the compressor inlet air to increase the compression efficiency in a liquid air energy storage and liquid natural gas (LNG) coupled system, which can offer large-scale energy storage with significantly improved exergy efficiency and round-trip efficiency. In this work, the effect of pressure of air, incline angle, and hydraulic diameter on the performance of a compressed air–water PCHE with a semicircle cross-section was studied. The results show that PCHE can realize the intermediate cooling of air compression in the liquid air energy storage system, and the pressure variation of air shows a limited effect on the heat transfer of PCHE; however, the hydraulic diameter and the incline angle both affect the heat transfer and the flow resistance of PCHE, and the best incline angle is 15°.

Numerical investigation on the performance characteristics of a novel biomimetic honeycomb fractal gas cooler of transcritical CO2 heat pump

In order to improve the heat transfer performance of the gas cooler in transcritical CO2 heat pump system, a novel biomimetic honeycomb fractal heat exchanger, with the advantages of great heat transfer efficiency and high compactness, is proposed for the transcritical CO2 heat pump in this study. Also, the conjugate heat transfer performance between supercritical CO2 and water in the novel gas cooler is investigated by the computational fluid dynamics method. The results firstly indicate that the difference of peak heat transfer coefficient in various flow channels reaches to 20.4% when the inlet flow flux of CO2 is 30 kg/(m2·s), significantly influenced by the uneven distribution of density and the secondary flow caused by buoyancy force. Secondly, when the flow flux of CO2 is 30 kg/(m2·s), compared with the horizontal flow, the heat transfer coefficients decrease by 11.4% and 40.7%, respectively, as CO2 flows vertically upward and downward. Finally, the heat transfer coefficient and comprehensive performance of the biomimetic honeycomb fractal heat exchanger are 144.6% and 20.4% higher than those of the printed circuit heat exchanger. The comprehensive performance of the 2nd and 3rd level biomimetic honeycomb fractal heat exchangers are 59.7% and 92.4% higher than that of the 1st level biomimetic honeycomb fractal heat exchanger.

Theoretical and numerical analysis of conjugate heat transfer for supercritical CO2 flowing in printed circuit heat exchanger

The printed circuit heat exchanger (PCHE) is often utilized for the supercritical CO2 (SCO2) Brayton cycle. This study proposed a assessed method with the dual effects of temperature and pressure to investigate the heat transfer performance (HTP) for PCHE derived from theoretical analysis and numerical validation. The influence of various operating conditions on total and hot-side heat transfer coefficient (HTC) was analyzed. The results showed that the PCHE may achieve better HTP when the critical index was near 1. The assessed way had been verified by utilizing the existing experimental data. The total and hot-side HTC for SCO2-Water PCHE were higher than that of SCO2-SCO2 PCHE, which may increase as cold-side Reynolds number increases. The effect of entropy generation rate for heat transfer on the irreversibility was larger than that of entropy generation rate for viscosity. This study may offer theoretical guidance for optimization of heat exchangers.

Impact of different types of channels on Thermo-hydraulic performance of a sodium-sCO2 Printed circuit heat exchanger for supercritical Brayton cycle applications

Supercritical CO2 has been proposed as a heat transfer fluid for Brayton cycles to achieve a high effectiveness in power generation from concentrated solar power plants. A printed circuit heat exchanger (PCHE) has been considered as an alternative design for a sodium to supercritical CO2 heat exchanger operating at high pressure and temperature (220 bar and 700 °C, respectively). Computational fluid dynamics has been used to compare the hydrothermal performance of different channel types and configurations to determine the most effective design for a 30 kW lab-scale system. The model was validated with relevant experimental conditions and the model was used to simulate 18 different channel types and configurations. The thermohydraulic performance of a single module of a PCHE comprising of counter-current passages for cold and hot flow, constructed out of Inconel, with different combinations of circular, semicircular, and rounded rectangular channels was systematically assessed. While straight channels were used for sodium, the hydrothermal performance of straight and wavy channels (with bending angles of 32.5° and 40°) were examined for the sCO2 side. A parametric analysis of a PCHE module with a fixed cross section (W = 6.5, H = 2.6 mm) showed the best performance for a 60 cm length with 2 g/s mass flow rate on the sodium side and 2.87 g/s on the sCO2 side. Using this outcome and limiting the maximum pressure drop to 2 % of the operating pressure at each side, the model showed that the best thermal performance (96.7 % effectiveness) was for a module with three 32.5° semicircular wavy sCO2 channels in conjunction with a straight circular sodium channel. The next highest thermal performance (96.4 % effectiveness) was achieved using a module with a straight rectangular channel for sodium and three wavy (32.5°) semicircular channels for sCO2. Using rectangular channels on both the hot and cold sides, a 96 % effectiveness was predicted between two 32.5° wavy channels for sCO2 and one straight channel for sodium.

Numerical simulation on heat transfer and flow of supercritical methane in printed circuit heat exchangers

The printed circuit heat exchanger (PCHE) is a novel type of heat exchanger in liquefied natural gas (LNG) industry. The gasification pressure of LNG in PCHE could exceed the critical pressure of methane, the main component of LNG. This paper established a series of three-dimensional models of PCHE units. The effects of structural parameters and channel shapes on the thermal hydraulic performance are studied. And new correlations to calculate the Nusselt number and Fanning factor of supercritical methane in straight and zigzag PCHEs are developed. For straight PCHE, the most influential geometrical parameters are the spacing between two adjacent channels in the plate and the diameter of the semicircle, which have been taken into account in the new correlation. For zigzag PCHE, the inclined angle has impact on both heat transfer coefficient and pressure drop while the pitch number only influences the pressure drop. Considering these factors, the new correlations for zigzag PCHE are modifications from the new straight PCHE correlations.

Mechanical Integrity of Printed Circuit Heat Exchanger

The printed circuit heat exchanger is a plate type heat exchanger with a high performance and compact size. Heat exchangers such as this need a unique form of bonding and other techniques to be used in their construction. In this study, the process of joining plates, diffusion bonding, was performed and studied. A special furnace was manufactured for bonding purposes. The bonding process of copper metal was carried out under specific conditions of a high temperature up to 700 oC, high pressure of 3.45 MPa, and in an inert environment (Argon gas) to make tensile samples. The tensile samples are cylindrical shapes containing groves representing the flow channels in the printed circuit heat exchanger and checking their tensile strength in addition to the standard shape of the tensile specimen to check the yield and ultimate strength of the copper. A higher tensile strength was obtained for diffusion bonded specimens than the yield strength of copper, up to 1.35 times the copper yield strength. The tensile strength decreases with the increase in the number of groves and the decrease in the distance between one grove and another. This is because the stress is concentrated in the sharp corners. A prototype heat exchanger of two plates and a header to be tested for its compressive strength was also manufactured. The results showed that the bond bears an air pressure of up to 8 bar without fail. It was also found to withstand a hydraulic pressure of up to 60 bar until it reached failure.

Study of thermal-hydraulics of a sinusoidal layered heat exchanger for MSR

Plate-type heat exchangers have been investigated as promising heat exchangers for molten salt reactors. It has been found that the heat transfer coefficient of complex channel geometries such that with S-shaped fins studied as printed circuit heat exchangers (PCHE) is generally very high. However, because there is a risk of blockage in the heat exchanger of the extremely small flow area for a molten salt reactor, a sinusoidal-shaped heat exchanger with a large flow area and a simpler shape has been selected. Thermal-hydraulic analyses of several types of flow channels have been performed using the FLUENT code. The turbulence model and the wall function selected in the present calculation were verified in advance by the experimental data. The calculated results were compared with the experimental results using the zigzag flow channels and experimental correlations. The computation results using FLUENT reproduce the empirical correlations previously obtained with smooth ducts for heat transfer and pressure drop. These comparisons also demonstrate that the turbulence model and the mesh of the computation in this study are appropriate. The proposed heat exchanger with a sinusoidal flow geometry is promising because the heat transfer coefficient is larger than that of the empirical correlation for a smooth duct and is almost the same as that of zigzag geometry. The heat transfer coefficient of the sinusoidal geometry is approximately twice as large as the Dittus and Boelter correlation. The friction factor is far below that of the zigzag geometry. In the case of a heat exchanger of this shape, it has been found from the extrapolation of the results of FLUENT that the number of channels required to remove heat of 175 MW is approximately 6000 sets of hot and cold channels. This result is also supported by a real-scale analysis using the RELAP5-3D code.

Experimental study on heat transfer performance of sCO2 near pseudo‐critical point in airfoil‐fin PCHE from viewpoint of average thermal‐resistance ratio

The printed circuit heat exchanger (PCHE) is one of the leading heat exchanger candidates in the supercritical carbon dioxide Brayton cycle, which has high efficiency and compactness. In the present paper, a novel type of PCHE with airfoil fins was proposed and tested. The effect of the thermal resistance variation on the heat transfer performance near the pseudo-critical point was analyzed. Meanwhile, a non-dimensional factor defined as the ratio of bulk temperature to the pseudo-critical temperature was applied to evaluate the heat transfer performance. The results indicate that the variation of the heat transfer performance can be attributed to the different average thermal-resistance ratios, where a larger the average thermal-resistance ratio corresponds to a better heat transfer performance. When the non-dimensional factor is around 1.03, the heat exchanger exhibits the highest heat transfer performance. In this regard, a working condition analysis method based on the non-dimensional factor and the average thermal-resistance ratio is suggested. Finally, a modified heat transfer correlation considering the non-dimensional working parameters near the pseudo-critical point is obtained.

Thermal–hydraulic characteristics and structure optimization of Z-channel printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is a compact equipment, which has the characteristic of high heat exchange efficiency. In practical application, the Z-type microchannel PCHE has shown unique advantage, and its structural parameters, such as pitch angle, pitch length, and channel diameter, have significant impact on its thermal–hydraulic characteristics. In this study, a series of PCHE models with a pitch angle of 5° to 45°, a pitch length of 12.3 mm to 24.6 mm, and a channel diameter of 1.25 mm to 2.25 mm are built by numerical method. Using a working medium of helium, we in detail analyze effects of these structural parameters of the PCHE on the related thermal–hydraulic characteristics. More importantly, to obtain the optimized structure of the PCHE, the response surface analysis of the simulation data is present. It shows that both the pitch angle and the inlet Reynolds number have greater effects on the flow and heat transfer performance of the PCHE. The quadratic polynomials of Nu and f are fitted by DesignExpert and the genetic algorithm is used for the multiobjective optimization. Three sets of optimized structures are given and also verified by the numerical simulations. The study could provide a guidance for the design and application of the PCHE in related engineering.

Numerical study of thermal-hydraulic performance of sCO2-molten salt printed circuit heat exchanger with discontinuous fins channel

Printed circuit heat exchanger (PCHE) is an essential part of supercritical CO2 (sCO2) Brayton cycle in the 3rd generation of concentrating solar power plant. Molten salt and sCO2 as the heat transfer fluid in PCHE, it is of great significance to improve its thermal and hydraulic performance. To reach this goal, two new discontinuous fin channels of PCHE were designed and their thermal-hydraulic performance was studied by numerical simulation. The results show that the second discontinuous fins channel with the best comprehensive thermal-hydraulic performance for sCO2, which has the Colburn j factor improvement by 2.1-4.6% and the Fanning friction factor f reduction by 3.8-6.4% compared with that of the airfoil fins; While the third discontinuous fins channel has the best hydraulic performance for both the heat transfer medium of molten salt and sCO2, among which the pressure drop per unit length and f have the largest reduction by 0.05-24.7% and 5.91-19.1% for sCO2, and by 25.62-29.39% and 1.35-2.4% for molten salt. As a result, the second and third discontinuous fins channel of PCHE are proposed to sCO2 and molten salt, respectively, which can contribute to design the PCHE for the 3rd generation of solar thermal power generation.

Predicting heat transfer and flow features of supercritical CO2 in printed circuit heat exchangers with novel wavy minichannels

Printed circuit heat exchangers (PCHEs) are unrivaled choices for heat exchange purposes in power cycles working with natural refrigerants such as carbon dioxide (CO2). Minichannels play a major role in heat transferring in these devices. They take up more than 95% of PCHEs volume; therefore, increasing the performance or compactness of PCHEs will be realized, provided that novel designs are adopted for the minichannels. In this study, the investigation of non-uniform wavy minichannels applying supercritical carbon dioxide (SCO2) as working fluid is carried out. To fulfill defined goals, a 3D conjugated model is developed to analyze the performance of novel geometries in both cooling and heating modes by considering the variations of SCO2's thermophysical properties. The results demonstrate that the proposed structures for the wavy minichannels create an upsurge in the heat transfer coefficient under the given operating conditions. It is explored that replacing the conventional wavy minichannel with the cases having short wavelengths at the upstream can increase the heat transfer enhancement factor from 36.1 to 51.1% in the cooling mode and from 40.8 to 56.5% in the heating mode. Furthermore, the larger the wave amplitudes at the upstream are, the more superiority it takes. Compared to all the proposed structures, the case with the largest wave amplitude and the smallest wavelength at the upstream attains the best overall performance. This structure of wavy minichannel can be utilized to manufacture highly efficient PCHEs with the capability of improving the overall performance index more than 1.5 times compared to the conventional wavy minichannel.